1. Field of the Invention
The present invention relates to an electrolyte electrode assembly including a pair of electrodes and an electrolyte interposed between the electrodes. Further, the present invention relates to a fuel cell including the electrolyte electrode assembly, and a pair of separators sandwiching the electrolyte electrode assembly.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs a solid polymer electrolyte membrane (electrolyte). The solid polymer electrolyte membrane is a polymer ion exchange membrane. In the fuel cell, an anode and a cathode each including an electrode catalyst layer and a porous carbon are provided on both sides of the solid polymer electrolyte membrane to form a membrane electrode assembly (electrolyte electrode assembly). The membrane electrode assembly is sandwiched between separators (bipolar plates) to form a unit cell. In use, normally a predetermined number of unit cells are stacked together to form a fuel cell stack, and the fuel cell stack is mounted in a vehicle, for example.
In general, in the membrane electrode assembly, the surface area of the solid polymer electrolyte membrane is larger than the surface areas of the anode and the cathode, and the outer end of the solid polymer electrolyte membrane protrude outwardly from the anode and the cathode. However, the mechanical strength of the solid polymer electrolyte membrane is low, and the outer end can be damaged easily.
In this regard, a solid polymer electrolyte fuel cell as disclosed in Japanese Laid-Open Patent Publication No. 05-242897 is known. As shown in FIG. 16, the fuel cell includes a membrane electrode assembly 3 including a solid polymer electrolyte membrane 1 and an anode 2a and a cathode 2b provided on both main surfaces of the solid polymer electrolyte membrane 1. The membrane electrode assembly 3 is sandwiched between reactant gas supply plates 4a, 4b. 
The reactant gas supply plate 4a has a fuel gas flow field 5a for supplying a fuel gas to the anode 2a, and the reactant gas supply plate 4b has an oxygen-containing gas flow field 5b for supplying an oxygen-containing gas to the cathode 2b. 
Gas seals 6a, 6b are provided between the membrane electrode assembly 3 and the reactant gas supply plates 4a, 4b. Reinforcement membranes 7a, 7b are provided between the gas seals 6a, 6b and the solid polymer electrolyte membrane 1.
In the case of forming a fuel cell stack by stacking a plurality of the fuel cells, reactant gas passages (not shown) extending in the stacking direction are formed in the outer ends of the reactant gas supply plates 4a, 4b. Further, the reactant gas passages for the fuel gas are connected to the fuel gas flow field 5a to supply the fuel gas to the fuel gas flow field 5a and the reactant gas passages for the oxygen-containing gas are connected to the oxygen-containing gas flow field 5b to supply the oxygen-containing gas to the oxygen-containing gas flow field 5b. The fuel cell stack adopts so called internal manifold structure.
In the structure, buffers needs to be provided between the reactant gas passages for the fuel gas and the fuel gas flow field 5a, and between the reactant gas passages for the oxygen-containing gas and the oxygen-containing gas flow field 5b for smoothly distributing the fuel gas and the oxygen-containing gas to the power generation surfaces.
However, in the fuel cell, the gas seals 6a, 6b are provided around the solid polymer electrolyte membrane 1 such that the reinforcement membranes 7a, 7b are interposed between the solid polymer electrolyte membrane 1 and the gas seals. Therefore, the cross sectional areas in the flow fields of the buffers become considerably small. Thus, the pressure losses due to concentration of the reactant gases become large, and it is not possible to supply the sufficient amount of the reactant gases to the power generation surfaces.